1. Technical Field
The present invention relates to a semiconductor device and a method and an apparatus for inspecting an appearance thereof.
2. Related Art
Sophistications and diversifications of semiconductor devices in recent years promote uses of various types of materials in diffusion processes for semiconductor wafers. New materials, which are newly employed for such processes, include films having lower adhesiveness or lower mechanical strength, and such materials may cause problems, in which mechanical shocks during wafer-dicing process create cracks between interconnect layers, leading to a progressing peeling-off of such material toward chips. Such problem becomes particularly considerable in dicing processes for semiconductor wafers that employ insulating films called “low-K film” having lower specific dielectric constant than that of SiO2 film.
When an assembly of chips having cracks therein is conducted, the cracks become worse by a heat stress in the assemble process to cause defects of flaking-off. Therefore, a precise detection of cracks in wafers after the dicing process greatly affects a reliability of the product.
In addition to above, related prior art documents for the present invention include Japanese Patent Laid-Open No. 2005-260,059 and Japanese Patent Laid-Open No. 2005-277,338.
In the actual manufacturing processes, a human visual inspection for an appearance of products or an automatic visual inspection with devices is conducted by employing a metaloscope or a stereomicroscope. In such case, focus is taken to a surface of a wafer.
When a crack is grown toward Z-direction (direction to be perpendicular to the surface of the substrate), the cracked piece is considerably inclined. Otherwise, the growth of the crack all the way eventually creates a chipped piece. As shown in FIG. 8, even if a polyimide film 203 is disposed above the wafer, if a crack 110 is proceeded all the way in Z direction, the polyimide film 203 is pushed up and is bent, as shown in plan view of FIG. 9. This reveals itself in a form of a discoloration 111 in its appearance, and thus, fortunately, a crack can be easily detected. In addition to above, in FIG. 8, the interconnect layer 202 and the polyimide film 203 are sequentially stacked on the silicon substrate 201.
However, when the crack is mainly grown only along x-y directions (direction along the surface of the substrate), the resultant step is relatively smaller of a height of less than several microns, and in such case, an identification of such crack is difficult, even if an observation is made with a precise focusing. Further, as shown in FIG. 10, if metal vias 112 (guard rings) are embedded in a portion, which is flaked-off, an identification of such crack can be achieved by an observation of the cross section, since a deformation 113 is occurred in that location. However, since the observation of the appearance is carried out from the above with a certain focusing, an obtained result of appearance 114 indicates no positional change of the metal or a slight bending of the inner metal (FIG. 11), and therefore it is very difficult to know a presence of a flaking-off in the wafer.
Since a manual observation, which depends upon a visual acuity of an operator, is carried out with a relatively lower accuracy, a detection of a flaked-off portion growing only along a direction of the surface of the substrate may not be excluded in the results of the observation, and thus a diffusion of the defects may be easily caused.
In general, in the case of directly and visually observing the cracks in the interconnect surface of the semiconductor chip, metaloscopes or stereomicroscopes are not suitable for sufficiently detecting the cracks, due to their lower magnifications, and therefore a scanning electron microscope (SEM) with higher magnification is necessary. However, an automation of the device for the visual inspection of the semiconductor chips in the mass production process by employing the SEM that requires an ultra-high-vacuum chamber is difficult to be achieved and provides increased manufacturing costs.